A29-15 Kinetics of Oxygen Deficit Build Up During Intermittent Exercise, Expressed by Phase Gain Analysis

Rationale At the start of exercise an O2 deficit is built up. The O2 deficit depends on the kinetic properties of the individual’s physiological system, e.g. on the adaptation ability to the new physiological state. The kinetic properties can be determined with phase and gain analysis during intermittent exercise. However, it can be expected that these properties are influenced by workload and body position. This study further investigates the interplay of phase angle and gain on the O2 deficit build up and the influence of workload and body position on this. Methods Ten healthy individuals performed four interval tests (6 x 1.5 minute of loaded exercise alternated with 6 x 1.5 minute of unloaded exercise), during which V’O2 was measured. Tests were conducted in a combination of either supine or upright position and at moderate or high workload. The gain and phase relations between O2 and workrate were calculated based on the imposed O2 fluctuations using MATLAB to assess their contribution to the O2 deficit. Statistical testing was done with a repeated measures ANOVA with post-hoc paired t-testing. Results Both gain and phase angle show a similar pattern across different test types, albeit in opposite direction (Figure 1). With higher workload the gain increases (p = 0.085 and p = 0.002) and phase difference (delay) decreases (p = 0.005 and p = 0.03) compared to moderate workrate. In supine position gain decreases and phase difference increases (all p < 0.05) compared to upright body position. Additionally, gain and phase angle show a linear relationship (R2=0.81 upright, R2=0.54 supine). Conclusions Due to the linear relationship of phase and gain, it can be expected that a lower phase difference will result in a higher gain. If phase difference becomes lower, reflecting a faster increase of O2 uptake, a higher V’O2 will be reached after 1.5 min and thus result in a higher gain (this is the case for any period until steady state is reached). With this in mind we can conclude the following: 1) Oxygen uptake shows less delay (phase difference) with higher workloads, also shown by a greater gain. This is most likely caused by a higher cardiac output and lower circulation time (and thus less delay) 2) During upright cycling, delays are also lower compared to supine cycling, again also reflected by the higher gain. These differences likely result from hemodynamic changes 3) Cycling in upright position at a higher workload will result in a lower oxygen deficit.